title: Seasonal sunshine and vitamin D: a possible explanation for differences in European and United States birth patterns.
abstract: This study tests whether seasonal differences in the United States and European sunshine is associated with human birth patterns. Birth data are adjusted for 31-day months, leap years, and an annual percentage. Clear observations and birth indices are correlated for European and U.S. cities. With 2-month exposure to clearness, r-values are Chicago (0.63), Bismarck (0.81), Dallas (0.86), Thessaloniki (0.66), and Copenhagen (0.54) and, with 3-month exposure, Amsterdam (0.69). Peak clearness occurs during the autumn for the United States and spring/summer for Europe. Differences in clearness may explain birth pattern differences and reduced U.S. births in the 1930s. Although the effect of vitamin D is plausible, further research is required.
authors.affiliation: bynehill@cableone.net
authors.forename: David R
authors.initials: DR
authors.lastname: Cummings
mesh_terms: D001723:Birth Rate / Q000639:trends; D005060:Europe; D005260:Female; D005306:Fertilization / Q000502:physiology*; D006801:Humans; D011247:Pregnancy; D018873:Pregnancy Rate / Q000639:trends; D012621:Seasons; D013472:Sunlight; D014481:United States; D014807:Vitamin D / Q000378:metabolism*
chemical_list: D014807:Vitamin D